It is a tendency in the art of braking vehicles to employ a rotary electric motor for supplying a service brake force. Behind this tendency there is a desire to use electricity for the control and actuation of different arrangements onboard the vehicle, thereby among other things obviating the need for pneumatic and/or hydraulic systems.
In such an electric service brake actuator there should normally be a device for converting the rotary motion from the electric motor to a translational movement suitable for the application of a brake pad or a brake shoe against a brake disc or a wheel rim or brake drum of the vehicle. Such a device can for example be a so-called ball screw (as is the case in a practical embodiment revealed herein).
The service braking is thus performed by means of electric power. In the possible absence of electric power normal service braking is not possible, and an emergency braking is desirable. Also, parking braking shall be performed by another arrangement than the service brake actuator.
The teachings herein are concerned with such a parking and emergency brake arrangement.
It is already known to employ a powerful clock spring for the purpose of delivering a rotary parking and emergency brake force through the above mentioned device for converting a rotary motion into a translational movement.
DE19945701A1 relates to a brake actuator, especially a brake actuator for rail vehicle brake calipers for a disc brake. The brake actuator comprises a service brake unit with an electromotive drive system for clamping and releasing the brake, a safety brake unit with a pre-loaded spring device for clamping the brake, and a brake spindle for converting the movements of the electromotive drive system into a translatory movement for activating a brake clamping mechanism; especially for activating brake calipers. The pre-loaded spring device and the brake spindle are positioned coaxially in relation to each other and are mechanically connected in series. The spring device comprises a coil spring that is arranged to directly engage the brake clamping mechanism. This calls for a large force being translated by the spring.
DE19617796A1 describes an electromechanical disc brake actuation device which has a spindle piston, loaded by an energy-storage spring coupled to a clamping piston for delivering the actuating force or stroke and engaging an axially non-displaceable female part by means of a non-self-locking adjusting thread. The spindle piston, under the force of the spring, can be screwed in the direction of actuation under electrical monitoring by means of a stepping motor, or a locking mechanism or similar, and the female part can be rotated to bring about the opposite direction of rotation of the spindle piston by an electric motor and a self-locking worm gearing. This enables the setting of relative rotations between the parts of the thread and hence rapid and controllable braking. The clamping piston includes an integrated wear adjustment device. The energy storing spring in this DE document is also a spring acting directly onto the braking means, and hence requires a large force spring, elbeit with a very limited motion.
CN103213597A relates to an electromagnetic controllable mechanical parking brake device which comprises action arms, an action arm installation seat, cylindrical compression springs, electromagnetic iron components and abrasion pieces. Two action arms are respectively connected on an upper end and a lower end of the action arm installation seat in a rotation mode, the cylindrical compression springs are arranged between the two action arms, two ends of each cylindrical compression spring are connected with the action arms on the upper side and the lower side respectively, the electromagnetic iron components are arranged inside the cylindrical compression springs and connected with the action arms on the upper side and the lower side, and two abrasion pieces are respectively arranged at the other end of each action arm.
Also in this CN document, the spring acts in an axial direction, and although the spring acts on levers connected to braking blocks, the force required by the spring is large. Compared to other prior art, electricity amount of the electromagnetic iron components is controlled to control frictional force among the abrasion pieces and a steel rail so as to achieve braking or parking of a vehicle, the abrasion pieces are compressed on the steel rail, most thermal load is born by the steel rail, the position of the vehicle is continuously moved, heat generated by the braking is rapidly dissipated on the steel rail, and the electromagnetic controllable mechanical brake parking device is suitable for being used for continuously-implemented brake of the vehicle on long-distance downhill.